The glycaemic index (GI) is a rating system for foods containing carbohydrates. It shows how quickly each food affects your blood sugar (glucose) level when that food is eaten on its own.

The glycaemic index (GI) is a rating system for foods containing carbohydrates. It shows how quickly each food affects your blood sugar (glucose) level when that food is eaten on its own.

High GI foods

Carbohydrate foods that are broken down quickly by your body and cause a rapid increase in blood glucose have a high GI rating. High GI foods include:

sugar and sugary foods

sugary soft drinks

white bread

potatoes

white rice

Low and medium GI foods

Low or medium GI foods are broken down more slowly and cause a gradual rise in blood sugar levels over time. They include:

some fruit and vegetables

pulses

wholegrain foods, such as porridge oats

Are low GI foods healthier?

Some low GI foods, such as wholegrain foods, fruit, vegetables, beans and lentils, are foods we should eat as part of a healthy balanced diet.

However, using the glycaemic index to decide whether foods or combinations of foods are healthy can be misleading. Foods with a high GI are not necessarily unhealthy and not all foods with a low GI are healthy. For example, watermelon and parsnips are high GI foods, while chocolate cake has a lower GI value.

Also, foods that contain or are cooked with fat and protein slow down the absorption of carbohydrate, lowering their GI. For example, crisps have a lower GI than potatoes cooked without fat. However, crisps are high in fat and should be eaten in moderation.

If you only eat foods with a low GI, your diet may be unbalanced and high in fat.

Can the glycaemic index help people with diabetes?

If you have diabetes, it’s useful to understand the glycaemic index, because eating foods with low GI ratings can help control blood glucose. However, other factors must also be taken into account. Research has shown that the amount of carbohydrate you eat, rather than its GI rating, has the biggest influence on blood glucose levels after meals.

It's also important to eat a healthy balanced diet that is low in fat, sugar and salt, and high in fruit and vegetables. If you’ve been advised to make changes to your diet, or you need advice, a diabetes dietitian can help you work out a diet plan. Speak to your GP about being referred to a dietitian.

Read government diet advice in the Eatwell Guide that shows the amounts of different types of foods needed to have a well-balanced and healthy diet. You don't need to achieve this balance with every meal but try to get the balance right over a day or even a week.